Pretty much, yeah. Same as grilling a burger and putting it on bread is cooking despite the bread being pre-made.

Afaik, cooking isn’t limited to applying heat to raw foods.

Might be worth saying that I don’t remember which dictionary the definition came from, and that dictionaries only record language, they don’t prevent changes over time. Which means that usage could have changed enough since the last time I looked at any, and now have a different usage added